vhdl-intelligent-tab

vhdl-intelligent-tab is a variable defined in `vhdl-mode.el'.
Its value is

t

Documentation:
Non-nil means `TAB' does indentation, word completion and tab insertion.
That is, if preceding character is part of a word then complete word,
else if not at beginning of line then insert tab,
else if last command was a `TAB' or `RET' then dedent one step,
else indent current line (i.e. `TAB' is bound to `vhdl-electric-tab').
If nil, TAB always indents current line (i.e. `TAB' is bound to
`indent-according-to-mode').

NOTE: Activate the new setting in a VHDL buffer by using the menu entry
"Activate Options".

You can customize this variable.